This invention relates generally to the field of gas desorption from metals; and, more particularly, to a method of enhancing the selective desorption of a particular isotope of a gas from metals. Enhanced selective desorption is especially useful in the operation of fusion devices.
A crucial element in realizing the high temperatures and fuel densities required for a successful fusion device is the control of plasma impurities. Also, to maximize fusion power output, fuel density must be optimized by controlling fuel recycling in conjunction with selective gas or pellet injection. A number of tokamak experiments have used Ti sublimated on the plasma confinement vessel walls to effect control of both hydrogen recycling (the hydrogen isotopes are the most promising fusion fuel) and impurities. A more promising alternative for hydrogen recycling and impurity removal is the Zr-Al non-evaporable bulk getter (manufactured by S.A.E.S. Getters, S.p.A.), which pumps hydrogen isotopes reversibly. This getter uses the alloy ST101 R (a mixture of Zr.sub.5 Al.sub.3 and Zr.sub.3 Al.sub.2) in the form of a powder press-bonded to a constantan heating substrate.
During normal operation, the getter pumps impurities irreversibly (sorbs only) and hydrogen isotopes reversibly (sorbs and desorbs). Impurities react chemically with the getter material forming stable products; whereas the hydrogen isotopes form a solution with the alloy. During sorption of gases, the surface of the getter material becomes saturated. Hence regeneration of the hydrogen isotopes from the getter material permits more impurities to be sorbed in subsequent operation. Regeneration of the hydrogen isotopes from the getter is accomplished by thermal desorption: the getter is heated to a high enough temperature to cause desorption, and the desorbed gas is pumped from the vessel. Since the hydrogen isotopes are diatomic molecules, thermal desorption is a second order kinetic process, which means that the desorption rate becomes asymptotically slow. Consequently, desorption involves considerable down-time and is often incomplete. This incomplete desorption can compromise reactor safety when tritium is one of the fuels. In addition, there are other circumstances, such as the need to perform helium leak detection following deuterium plasma operation, for which the incomplete desorption has deleterious consequences as well.
Therefore, it is an object of the present invention to enhance the desorption of a selected isotope from metals.
It is also an object of the present invention to increase the amount of the selected isotope desorbed from a metal, while decreasing the desorption time.
It is yet another object of the present invention to enhance the selective desorption of the hydrogen isotopes from metals.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.